Telescope Takes Sharpest Pictures of Space Yet From Earth

The movable secondary mirror on the Large Binocular Telescope during its installation in the Arcetri lab. The image shows the 672 tiny magnets spread over the back of the mirror. The reflecting face of the mirror is face down. The
upper portion contains the electro-mechanical devices that control the magnets.Credit: R. Cerisola

A telescope in Arizona has taken the sharpest pictures yet
of deep space from Earth with a new system that provides a level of clarity
never seen before.

The technology relies on adaptive
optics ? a mechanism that allows a telescope's mirror to bend in order to
compensate for the blurring of light as it passes through the Earth's
atmosphere.

The new system, installed on the $120 million Large
Binocular Telescope (LBT) on Mount Graham in Arizona, has delivered images three
times sharper than the Hubble Space Telescope, LBT scientists said. And that's
with only one of its twin 27.6-foot (8.4-meter) mirrors working.

"The results on the first night were so extraordinary
that we thought it might be a fluke, but every night since then the adaptive optics
have continued to exceed all expectations," said astronomer Simone
Esposito, leader of a team from Italy?s Arcetri Observatory of the Istituto Nazionale
di Astrofisica (INAF). "These results were achieved using only one of
LBT?s mirrors. Imagine the potential when we have adaptive optics on both of
LBT?s giant eyes."

INAF collaborated with the University of Arizona?s Steward
Observatory to build the adaptive optics device, called the First Light
Adaptive Optics system (FLAO).

The Hubble Space Telescope has achieved groundbreaking
images thanks to its perch above Earth's atmosphere. It and other space
telescopes also have another advantage over ground-based observatories: They
can focus on one celestial object for hours or even days, steadily collecting
light to form a brighter image.

Bad weather can often interrupt observing sessions from
Earth, and even under perfectly clear conditions, a ground-based optical telescope
scanning the night sky must stop observing when the sun rises.

Yet the Hubble telescope
itself ? with a main mirror 7.9 feet (2.4 meters) wide ? is somewhat small
compared to the largest ground-based observatories. However, those Earth-bound
telescopes are hampered by the atmosphere, which blurs light passing through
much the way water blurs the view from the bottom of a swimming pool.

That's where adaptive optics come in.

The LBT has a 3-foot (0.91-meter) wide secondary mirror
built in. This mirror, only 0.06 inches (1.6 millimeters) thick, is so pliable
that it can easily be bent by devices pushing on the 672 tiny magnets glued to its
back.

A special sensor detects atmospheric distortions in real
time and controls the mirror to adjust its position to compensate, effectively
canceling out the blurring. The mirror can make adjustments every one-thousandth
of a second, with accuracy to better than ten nanometers (a nanometer is one
millionth the size of a millimeter).

Astronomers measure image sharpness with a term called the
Strehl ratio, where 100 percent would be a perfect image. Without adaptive
optics, most ground-based observatories have a Strehl ratio of less than 1
percent.

With the new system, the LBT has achieved peak Strehl ratios
of 82 to 84 percent.

"This is an incredibly exciting time as this new
adaptive optics system allows us to achieve our potential as the world?s most
powerful optical telescope," said Richard Green, director of the LBT.
"The successful results show that the next generation of astronomy has
arrived, while providing a glimpse of the awesome potential the LBT will be
capable of for years to come."